Conventionally, as an illumination device there is a type of lighting equipment called “wall washer”, which radiates a lot of light onto a wall or the like (for example, see patent literature 1). Further, a spotlight is included in the illumination device, which is to illuminate a specific area (spot) in a focused manner to attract an audience's attention in a theater and so forth.
Conventionally, a halogen lamp has been often used as a light source for such illumination devices. However, in recent years, an LED is increasingly used in accordance with the request for long operating life, energy saving and so forth. In particular, in an illumination device employing as a light source a multi-color light emitting diode (full color light emitting diode included), which is constituted by a plurality of LED chips with mutually different light emitting colors, various colors can be created and further, for example color temperature and color tone can be changed as well by changing the output of each LED chip.
However, since the multi-color light emitting diode generally includes LED chips such as R (red) chip, G (green) chip, and B (blue) chip, which are housed in a single package to form a resin molded structure as a whole (for example, see patent literature 2), even when white light emission is intended to be created by using RGB color mixing, the RGB color light cannot be well mixed and may be individually seen as respective colors of R, G and B. Further, due to the separation of the light emission colors as described above, color inconsistency may unfavorably occur in the light irradiated onto an object to be irradiated.
Further in a conventional spotlight, a plurality of light emitting diodes is obliquely disposed on a curved surface and irradiation light from each light emitting diode is concentrated on one point to form a virtual single point light source unit, and the light emitted from the light source unit is guided to pass through an aperture to radiate (for example, see patent literatures 3 and 4).
In such a spotlight, although undiffused light is preferably created by using an aperture having the smallest possible size of hole in order to effectively irradiate a certain area (spot) with the light emitted from a light source, if there is less diffusion, the mixture of light becomes insufficient, which may cause color inconsistency to occur more easily. As such, although a lens can be provided to facilitate mixture, the configuration is inefficient.
Specifically, in the aforementioned spotlight, in order to focus on one point the irradiation light from the plurality of light emitting diodes, each light emitting diode is obliquely fixed so as to incline the optical axis of the irradiation light from each light emitting diode. For this purpose, an inclined plane or a curved surface needs to be formed for a substrate for attaching a light emitting diode thereto and a heat sink for dissipating heat from a light emitting diode, and the process is not easy.
Further, such as when irradiating pictures exhibited in a museum, depending on pictures vertically long or horizontally long, in order to efficiently irradiate an object to be irradiated in the longitudinal direction thereof with light having little color inconsistency, it is desired to make changeable a degree of light diffusion in the vertical and horizontal directions in accordance with an object to be irradiated.